Method of grinding a surface of a workpiece and a tool for carrying out the method

ABSTRACT

Grinding a surface of a workpiece with abrasive particles by impregnating a pad of reticulated foam-like material with the abrasive particles, whereby the abrasive particles occupy interstices in the foam-like material, the abrasive particles and the foam-like material respectively having hardnesses greater and less than that of the workpiece surface; effecting relative rubbing movement between the pad and the workpiece, whereby the foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles in the rubbing surface of the pad and to open interstices in the foam-like material of the pad to the rubbing surface thereof, and applying a liquid to the rubbing surface of the pad, whereby material worn away from the pad and the workpiece during the rubbing action will be washed from the rubbing surface of the pad, through the opened interstices in the pad of foam-like material. Only some of the interstices in the pad are occupied by abrasive particles and those interstices which are not occupied by abrasive particles intercommunicate to define a continuous throughway extending between the rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through which said washing liquid can flow to or from the rubbing surface.

i United States Patent [191 Jury et al.

[ Nov. 11, 1975 METHOD OF GRINDING A SURFACE OF A WORKPIECE AND A TOOL FOR CARRYING OUT THE METHOD [75] Inventors: Kenneth James Jury; Brian John Mottram, both of Coventry, England [73] Assignee: Ryton Machine Tools (Coventry) Limited, Coventry, England [22] Filed: Feb. 28, 1974 [21] Appl. N0.: 446,918

[30] Foreign Application Priority Data Aug. 9. 1973 United Kingdom 37809/73 [56] References Cited UNITED STATES PATENTS 3,252,775 5/1966 TocciGuilbert 51/296 3,607,159 9/1971 Haywood 51/296 3,701,703 10/1972 Zimmer etal. 5l/297 Primar ExanzinerOthell M. Simpson Attorney, Agent, or FirnzEdward F. Connors [57] ABSTRACT Grinding a surface of a workpiece with abrasive particles by impregnating a pad of reticulated foam-like material with the abrasive particles, whereby the abrasive particles occupy interstices in the foam-like material, the abrasive particles and the foam-like material respectively having hardnesses greater and less than that of the workpiece surface; effecting relative rubbing movement between the pad and the workpiece, whereby the foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles in the rubbing surface of the pad and to open interstices in the foam-like material of the pad to the rubbing surface thereof, and applying a liquid to the rubbing surface of the pad, whereby material worn away from the pad and the workpiece during the rubbing action will be washed from the rubbing surface of the pad, through the opened interstices in the pad of foam-like material. Only some of the interstices in the pad are occupied by abrasive particles and those interstices which are not occupied by abrasive particles intercommunicateto define a continuous throughway extending between the rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through which said washing liquid can flow to or from the rubbing surface.

5 Claims, 13 Drawing Figures US. Patent Nov. 11,1975 SheetlOfS 3,918,220

U.S. Patent Nov .11 ,1975 Sheet30f5 7' 3,918,220

U.S. Patent Nov. 11, 1975 Sheet 4 f5 3,918,220

US. Patent Nov. 11, 1975 Sheet 5 of5 3,918,220

FIG. 13

METHOD OF GRINDING A SURFACE OF A WORKPIECE AND A TOOL FOR CARRYING OUT THE METHOD The invention relates to a method of grinding the surface of a workpiece with abrasive particles and a tool for carrying out the method. The term "grinding" as used herein is intended to means any grinding action by abrasive particles and includes fine surface finishing and polishing where the grit size is very small. I

A disadvantage of known grinding tools is that the grinding surface of the tool rapidly becomes clogged with material from the tool and the workpiece surface, thereby impairing the efficiency of grinding and the finish of the workpiece surface. An object of the invention is to provide a method and a tool by which the grinding surface of the tool is kept clear of material removed from the tool and the workpiece, thereby prolonging the effective life of the tool and improving the finish of the workpiece surface and also permitting the relative speeds of movement of the tool and the workpiece to be higher and for the grinding to be effected at greater pressure than hitherto.

According to the invention, a method of grinding a surface of a workpiece with abrasive particles consists in the steps of impregnating a pad of reticulated foamlike material with the abrasive particles, whereby the abrasive particles occupy interstices in the foam-like material, the abrasive particles and the foam-like material respectively having hardnesses greater and less than that of the workpiece surface; effecting relative rubbing movement between the pad and the workpiece, whereby the foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles in the rubbing surface of the pad and to open interstices in the foam-like material of the pad to the rubbing surface thereof, and applying a liquid to the rubbing surface of the pad, whereby material worn away from the pad and the workpiece during the rubbing action will be washed from the rubbing surface of the pad, through the opened interstices in the pad of foam-like material.

Preferably only some of the interstices in the pad are occupied by abrasive particles and those interstices which are notoccupied by abrasive particles intercommunicate to define a continuous throughway extending between the rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through which said washing liquid can flow to or from the rubbing surface.

Conveniently said washing liquid is injected through the unoccupied interstices from a face of the pad remote from the rubbing face thereof and the liquid is allowed to flow away from the rubbing face through the opened interstices therein.

The invention also includes a grinding tool comprising a pad of reticulated foam-like material impregnated with abrasive particles, whereby the abrasive particles occupy interstices in the foam-like material, the abrasive particles and the foam-like material respectively having hardnesses greater and less than that of the surface of the workpiece which is to be ground, whereby the foam-like material will be worn away during the,

rubbing movement to expose fresh abrasive particles in the rubbing surface of the pad and to open interstices in v the foam-like material leading from the rubbing surface of the pad to convey liquid applied to the rubbing sur- 2 face of the pad to wash away from the rubbing surface of the pad material worn from the pad and the workpiece during the rubbing action through the opened interstices in the pad.

The grinding tool may include a support member in which the pad of reticulated foam-like material is mounted.

The pad may be shaped to conform with the surface of the workpiece to be ground. Where the pad is shaped to conform with the surface of the workpiece to be ground, the pad may be pre-shaped before its impregnation with the abrasive particles.

The abrasive particles may be of any suitable hard material for example diamond, a synthetic or natural substance usually used for grinding, such as silicon nitride, silicon carbide or aluminium oxide, or a hard alloy steel, such as a nickel-chromium alloy steel.

The support member may be provided with an inlet or outlet port through which said washing liquid is passed, the port communicating with a continuous throughway defined in the pad and extending between the rubbing surface of the pad and a face thereof remote from said rubbing surface, the continuous throughway being defined by intercommunicating interstices that are not occupied by abrasive particles.

The invention also includes a method of manufacturing a grinding tool as set out in any one of the five immediately preceding paragraphs in which a reticulated foam-like material is impregnated with the abrasive particles.

The abrasive particles may be injected into interstices of the foam-like material under pressure together with a bonding material which is then allowed to set to hold the abrasive particles in the foam-like material. The bonding material may be a synthetic resin, for example, of an epoxy type resin or it may for example be a ceramic material.

Alternatively the abrasive particles may be injected into interstices of the foam-like material and bonded to the foam-like material by subjecting the latter to a sintering process. Conveniently the abrasive particles may be distributed through the foam-like material priorto sintering by vibrating the foam-like material. The foamlike material is such that it will withstand heating to the temperature required to sinter the abrasive particles to the foam-like material.

In yet another method of manufacturing the pad of the grinding tool, the abrasive particles may be secured to the foam-like material by a metallic plating process and therefore prior to injecting the abrasive particles into interstices in the foam-like material, the walls of the interstices are given ametallic plating. The plating process may be of any suitable kind. For example it may be an ,electrolytic plating process, an electroless plating process, that is the deposition ofa metallic layer from a metallic salt solution in which the pad together with impregnated abrasive particles is immersed, or a vacuum deposition process.

Where the abrasive particles are particles of diamond, they would be pre-coated with a metallic layer before being bonded by the metallic plating process to the foam-like material. Alternatively where the particles are of tungsten carbide or similar abrasive material, they may not need to be pre-plated.

In yet another method of manufacturing the pad of the grinding tool, the abrasive particles may be secured to the foam-like material by a metallic flame-spraying process. The abrasive particles may be injected into the interstices of the foam-like material before applying the flame-spraying process. Alternatively, the abrasive particles may be applied to the foam-like material in the metal spray which will permeate through interstices in the foam-like material. For example, the flame-spraying process may be performed by a thermo-spray powder gun to which the abrasive particles are supplied as in a thermo-spray or plasma spray process, the abrasive particles being of such material that they do not become molten in the flame.

In any of the foregoing methods of manufacturing the pad of the grinding tool, a removable mask may be employed to limit the injection of abrasive particles to certain regions of the pad.

By way of example, the polishing or grinding tools in accordance with the invention, their construction and use will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagram, to a large scale, of a pad forming the tool;

FIGS. 2 to 5 are diagrams showing different ways of impregnating a foam-like pad with abrasive particles;

FIG. 6 is a diagram showing generally the way in which a pad is mounted and used to perform a polishing or grinding operation;

FIG. 7 is a cross-section through the pad, its mounting and a workpiece on the plane VII-VII in FIG. 6;

FIG. 8 is a cross-section through a first practical embodiment of tool in accordance with the invention;

FIG. 9 is a view of the tool in the direction of arrow IX inFIG. 8;

FIG. 10 is a section on the line XX in FIG. 11 ofa second practical embodiment of tool in accordance with the invention;

FIG. 11 is a section on the line XI-XI in FIG. 10;

FIG. 12 is a view in the direction of arrow XII in FIG. 11 of the pad employed in the tool shown in FIGS. 10 and 11, and

FIG. I3 is a view similar to FIG. 10 of a modification of the second practical embodiment of the tool.

The tool essentially comprises a pad of reticulated foam-like material having a multiplicity of randomlydisposed interstices therein in which particles of abrasions are embedded. Such a foam-like material is called metal foam. Metal foam known by the Registered Trade Mark RETIMET is described in British Patent Specification No. 1,199,404 of Foam Metal Limited and is made from a reticulated synthetic plastics foam which is coated throughout the wall surfaces defining the interstices in the foam with metal by, for example, electrodeposition after making the foam electrically conductive. The plastics foam may be left within the metal coating or it may be destroyed to leave the metallic coating as a sketetal structure. The metallic coating may be of any metal to which the abrasive particles which are to be embedded in the interstices of the foam-like material, in accordance with this invention, can be bonded as hereinafter described. For example, nickel, copper and lead have been used. The foam-like material must also have a hardness less than that of the abrasive particles and that of the workpiece to be ground.

The abrasive particles may be of diamond, any natural or synthetic material usually employed as a grinding material, such as silicon oxide, silicon carbide, silicon nitride, aluminium oxide or boron nitride, or a hard alloy steel, such as a nickel-chromium alloy steel. The abrasive particles selected must have a hardness greater than that of the foam-like material and the workpiece. The abrasive particles are bonded in interstices of the pad of foam-like material by any of the methods to be described hereinafter. When a surface of the pad is rubbed against a surface ofa workpiece by a grinding movement, abrasive particles and particles of the workpiece material will be separated from the rubbing surfaces of the pad and the workpiece respectively and are washed away by a liquid, for example, a coolant, the interstices in the pad are opened by the removal of abrasive particles by the rubbing action aiding the flow of the washing liquid to or from the rubbing surfaces. The foam-like material will also be rubbed away and this will open more interstices and will expose fresh abrasive particles in the rubbing face of the pad. Thus throughout the grinding operation a layer of fresh abrasive particles in the rubbing surface will continually be exposed.

The impregnation of the interstices in the pad with abrasive particles may be substantially complete, that is most interstices contain an abrasive particle. Alternatively only some of the interstices, for example, are filled with abrasive particles, the interstices containing abrasive particles being randomly-disposed throughout the pad and the urn-occupied interstices communicating with one another to define continuous throughways from a face of the block remote from the rubbing face to the rubbing face. Before using the pad, it is mounted in or secured to a mounting block or backing member. Where the pad is of the kind which has been only partly impregnated with abrasive particles, a face of the pad remote from the rubbing face, for example the back face, communicates with a port in the mounting block or backing member. The washing fluid is then passed through the port and the unoccupied interstices to flow through the rubbing surface of the pad and will from there wash away from the rubbing surfaces particles from the pad and the workpiece. Alternatively washing fluid supplied directly to the rubbing faces may be retained within a seal enclosing the area of the rubbing face and be removed through the un-occupied interstices in the block and through the port in the mounting block or backing member. Where the pad is of the kind that is substantially filled with abrasive particles, it would be held in a mounting block or on a backing plate side-by-side with a pad in which the interstices have not been filled with abrasive particles, i.e., they have been left un-occupied, washing liquid being passed through the interstices of the latter pad between a port in the mounting block or backing plate and the rubbing surfaces of the two pads.

A diagrammatic perspective view of a pad, to a large scale, impregnated with abrasive particles is shown in FIG. 1. The pad 10 is a reticulated foam-like material having randomly-disposed intercommunicating interstices 11 therein. Some of the interstices are shown occupied by abrasive particles 12 bonded to the walls defining the interstices at 13.

Several methods of impregnating a pad of the foamlike material with abrasive particles are now described with reference to FIGS. 2 to 5.

FIG. 2 shows diagrammatically how a pad of premade foam metal is impregnated with a mixture of abrasive particles, resin and hardener, where the abrasive particles are to be held in interstices in the foam metal by the resin. An openable mould 15 has a cavity 16 therein of a shape and size to receive the pre-formed pad 17. The cavity has an inlet port 18 through which the mixture is applied and an outlet port 19, fitting with a controlling bleed screw 20 through which displaced air and, in some cases, water is expelled during the impregnation. The inlet port 18 communicates with a ram 21 into the cylinder of which the mixture is inserted through plug 22. The mixture of, abrasive particles, resin and hardener, together with water where an emulsion is easier to inject, is inserted into the cylinder of the ram 21. The preformed pad 17 of foam metal is placed in the cavity 16 and the ram 21 is connected to the mould 15. The bleed screw 20 is suitably adjusted and the ram is operated to displace the mixture into the interstices of the foam metal. The mould 15 is opened and the pad 17 is removed and allowed to dry in air or is heated, thereby to cure the resin. The extent of impregnation of abrasive particles in the foam metal may be controlled by varying the volume ratio of the total mixture to the cubic capacity of the foam metal, the ratio of the volume of abrasive particles to the combined volume of resin and hardener in the mixture, the pressure applied by the ram or the time of application of the pressure or any combination of these factors. For example where the preformed pad of foam metal is metal (or plastics wall coated with metal) and 90% air space, 85 of the total volume may be filled with the mixture (made from 70% of the whole volume of abrasive particles, 10% of the whole volume of resin and 5% of the whole volume of hardener). The resulting pad will then have 5% of its total volume formed by un-occupied interstices. It has been found that these interstices are randomly-disposed throughout the pad and providing there are sufficient un-occupied interstices these will be in communication with one another in a random arrangement of throughways extending between the faces of the pad. I I

FIG. 3 is a diagram similar to FIG. 2 showing a combined mould and ram for impregnating a tubular preformed pad of foammetal. The pad may be circular or rectangular in cross-sectional shape. A cylinder 25 defining the combined mould and ram cylinder has removable end plates 26 and 27 and an internal bore of the outer shape of the preformed pad. The cylinder 25 contains a piston 28 of appropriate cross-sectional shape and a hub 29 shaped to define the internal crosssectional shape of the preformed pad. The preformed pad 30 is placed in an annular space 31 between the cylinder 25 and the hub 29. As before, a bleed screw 32 controls flow of air or water through a port 33 in the end plate 26 of the cylinder 25 and communicating through a duct 34 with the annular space 31. The mixture of abrasive particles, resin and hardener is inserted into the cylinder adjacent the end of the pad 30 and hub 29 as shown at 36. The piston 28 and end plate 27 are placed in the positions shown and pressure is applied to inject the mixture into the pad, asdescribed with reference to FIG. 2. The pad is then removed for curing of the resin.

Instead of using a resin and hardener, the abrasive particles may be mixed with a ceramic material which after injection into the mould is allowed to harden or is fired.

FIG. 4 shows a combined mould and resin similar to FIG. 3, but intended for impregnating a block instead of a tubular pad and thus not including the hub 29. Instead a mask 35 is located in the cylinder 25 between the piston 28 and the pad 30. The mask has a pattern of apertures formed therein whereby the mixture will only be injected through the holes in the mask 35 and so the interstices directly behind the apertures in the mask will be filled with the mixture. According to the pressure applied and the time of application, there will be a tendency for the mixture to permeate into interstices behind the non-apertured parts of the mask, but this tendency can be controlled. The use of a mask therefore enables the interstices in some portion of the pad to be left un-occupied.

FIG. 5 shows how a preformed pad can have abrasive particles injected into it where the particles are to be secured in the pad by sintering. A preformed pad 40 of foam metal is inserted into a cavity 41 in a floating die 42. The bottom of the cavity is closed by a fixed punch member 43. Abrasive particles mixed with a powder which can be sintered to the abrasive particles and the foam metal are poured into the cavity 41 on top of the pad '40 as shown at 46. A top punch member 44 is then inserted into the cavity in the floating die 42. The die is vibrated by an electro-magnetic vibrator 45 to cause the mixture to permeate through the interstices of the pad. Pressure is applied to the pad to effect compression of the mixture therein. The impregnated pad is then removed and placed in a sintering furnace where the metal powder becomes sintered to the abrasive particles and to the metal foam.

As aforesaid, other methods of impregnating and securing abrasive particles in the pad of foam-like material may be employed. For example the foam-like material may be plated, if not already coated with a suitable metal, and the abrasive particles may be plated to the metallic coating of the foam-like material by a plating process which may be electrolytic, electroless or by vacuum deposition. A mask may be used to limit the plating to only certain regions of the pad.

Alternatively the abrasive particles may be introduced as a mixture with a metal powder, as described with reference to-FIG. 5 and then be sintered by flamespraying or a mixture of abrasive particles and metal powder may be introduced by a flame gun as in a flamespraying process. A mask may be used to limit the flame-spraying to certain areas of the pad.

The impregnated pad may be of any shape depending upon the grinding operation to be performed. For example it may be a block having a concave surface for polishing the cylindrical surface of a shaft or it may be a flat pad for polishing a flat surface, it may be annular or in the form of a rounded tool for polishing an internal surface or it may be formed as a wheel. By way of example only, a pad 50 is shown in FIGS. 6 and 7 having a concave rubbing face for polishing the cylindrical surface of a shaft 51. The polishing may be effected by relative rotation or transverse movement, relative longitudinal vibration or feeding between the pad and the shaft while pressure is applied to the pad.

The pad is held by a backing member to which it is secured, for example by bonding, orit may be held in a mounting block. A suitable backing member 52 is shown in FIGS. 6 and 7. The backing member may have a port 53 therein communicating with a duct 54 to which a liquid lubricant or coolant is applied. The liquid may be water or any other suitable liquid. The liquid flows through interstices in the pad that are not occupied by abrasive particles. As these intercommunicate within the pad, as already described, the liquid will flow through the pad to the rubbing surface 55 thereof and will wash away particles of abrasive and foam metal worn away from the pad and particles worn from the workpiece during the rubbing action. Fresh abra- 7 sive particles are continually being exposed in the rubbing surface 55 of the pad.

Three practical arrangements of mounting a pad for polishing a cylindrical shaft or roll that the Applicants have employed are now described with reference to FIGS. 8 and 9; FIGS. 10 to 12, and FIG. 13.

Referring firstly to FIGS. 8 and 9, the pad comprises a plurality of alternate elements 60, 61 clamped together side-by-side. The elements 60 are made of foam metal which has been substantially completely impregnated with abrasive particles, that is as many as possible of the interstices in the pad have been filled with abrasive particles; whereas the elements 61 are of unimpregnated metal foam. The elements 60, 61 are clamped together to form a lozenge-shaped insert between two metal plates 62 secured together through the elements by screws. The insert is held in a complementarily-shaped socket 65 in a mounting block 63 by a retaining plate 64. The bottom of the socket 65 communicates with a duct 66 to a port 67 to which a supply pipe for admitting liquid coolant is connected. The rubbing faces 68 of the elements 60, 61 are shaped to conform to the surface of the shaft 69 or roll to be polished. The mounting block is shown secured to a support 70 in FIG. 8. The tool is used in rotating the shaft 69 while applying a force on the support 70 to urge the pad into contact with the surface of the shaft 69. The support 70 may also be moved parallel to the axis of the shaft 69 to produce a relative reciprocation or feeding movement longitudinally of the shaft 69. During the polishing operation, the liquid coolant supplied to the mounting block 63 passes through the interstices of the elements 61 to their rubbing faces 68 and from there spreads all over the rubbing faces 68 of the elements of the whole insert to emerge from the periphery of the insert adjacent the surface of the shaft 69. The liquid coolant therefore washes away abrasive particles and particles of the foam metal and also particles of the shaft worn away by the polishing operation. During the polishing operation fresh abrasive particles are continually being exposed in the rubbing faces 68 of the elements 60.

Referring to FIGS. 10 to 12, a pad 70 of foam metal impregnated with abrasive particles, as described hereinbefore, is bonded to a curved backing plate 71 carried on a spigot 72 having a duct 73 therein communicating with a liquid coolant supply pipe 74. The spigot 72 is held in a block 75 to which a pair of plates 76 are pivoted by pins 77. The ends of the plates 76 remote from the pivot pins 77 carry pins 78 to which the backing plate 71 is secured. Coolant supplied through the pipe 74 passes to a hole 79 in the pad and from there percolates through un-occupied interstices and along the rubbing face of the pad to remove worn particles from the rubbing face. Fresh abrasive particles are continually exposed in the rubbing face as abrasive particles break away from the foam metal and the latter is worn away. The abrasive particles may be disposed throughout the pad provided sufficient un-occupied interstices are left therein for the flow of coolant to the rubbing face or they may be disposed only in certain regions of the pad behind certain areas 80 of the rubbing face, as shown in FIG. 12. This pattern of regions occupied by abrasive particles may be produced by a mask, as hereinbefore described.

Finally, FIG. 13 shows a pad arrangement similar to that shown in FIGS. 10 to 12 in which the pad 70 and backing plate 71 are enveloped in a seal comprising a deformable tube 81 extending around the periphery of the pad and carried by a flexible skirt 82 secured to the plates 76. A coolant extraction pipe 83 extends from the space within the seal to a coolant outlet pipe carried on the block and leading to an extractor pump (not shown). Thus coolant after washing away the particles from the rubbing face is carried together with the particles to the pump. The particles can then be filtered from the coolant and the coolant re-circulated.

As a modification of the arrangement shown in FIG. 13 the pad could be provided with a region containing un-occupied interstices separated from the remainder of the pad through which the coolant can be returned, instead of the extraction pipe 83 being provided. In a further modification the coolant could be applied directly through the pipe 83, allowed to travel through opened interstices in the rubbing face and then extracted through un-occupied interstices in the pad to the hole 79 and from there extracted through the duct 72 and pipe 74.

In the foregoing embodiments, as the abrasive particles at the rubbing surface of the pad are continually exposed during the polishing or grinding process and the materials worn away from the tool and the workpiece are continually washed through the interstices in the pad, the tool will not readily become clogged and thus the effective life of the tool and the finish of the workpiece will be improved. Furthermore the liquid will be distributed throughout the rubbing surface of the pad and so the speed of the grinding movement and the pressure applied to the tool can be greater than hitherto, all these factors resulting in an improved finish. By selecting different tools having pads impregnated with abrasive particles of different hardness and grit size, any desired surface finish can be produced.

What we claim as our invention and desire to secure by Letter Patent of the United States is:

1. A method of grinding a surface of a workpiece with abrasive particle-s consisting in the steps of impregnating a pad of reticulated foam-like material having a plurality of interstices therein with said abrasive particles. said abrasive particles occupying only some of said interstices, said abrasive particles and said foamlike material respectively having hardnesses greater and less than that of the workpiece surface and those interstices which are unoccupied by said abrasive parti cles intercommunicating to define a continuous throughway extending between a rubbing surface of the pad and a face thereof remote from said rubbing sur face, thereby to define a path through said pad for washing liquid applied thereto, effecting relative rubbing movement between said pad and the workpiece, whereby said foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles and said unoccupied interstices in said rubbing surface of said pad, and applying said washing liquid to said rubbing surface of said pad, whereby material worn away from said pad and from the workpiece during the rubbing action will be washed from said rubbing surface of said pad by said washing liquid flowing through said unoccupied interstices in said pad.

2. A method of grinding according to claim 1 in which said washing liquid is injected through said unoccupied interstices from said face of said pad remote from said rubbing face thereof and said washing liquid is allowed to flow away from said rubbing face through said exposed unoccupied interstices therein.

3. A grinding tool comprising a pad of reticulated foam-like material having a plurality of interstices therein of which interstices only some are impregnated with abrasive particles, said abrasive particles and said foam-like material respectively having hardnesses greater and less than that of the surface of a workpiece which is to be ground, and those interstices which are unoccupied by said abrasive particles intercommunicating to define a continuous throughway extending between a rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through said pad for washing liquid applied thereto, whereby on effecting relative rubbing movement between said pad and the workpiece said foamlike material will be worn away during the rubbing movement to expose fresh abrasive particles and said unoccupied interstices in the rubbing surface of said pad, and a support member in which said pad of foamlike material is mounted, said support member having a port therein through which said washing liquid is passed, said port communicating with said continuous throughway defined in said pad, whereby material worn away from said pad and from the workpiece during the rubbing action will be washed from said rubbing surface of said pad by said washing liquid flowing through said unoccupied interstices in said pad.

4. A grinding tool as claimed in claim 3 in which said pad is shaped to conform with the surface of the workpiece to be ground.

5. A grinding tool as claimed in claim 4 in which said pad is pre-shaped before the impregnation of interstices therein with said abrasive particles. 

1. A method of grinding a surface of a workpiece with abrasive particles consisting in the steps of impregnating a pad of reticulated foam-like material having a plurality of interstices therein with said abrasive particles, said abrasive particles occupying only some of said interstices, said abrasive particles and said foam-like material respectively having hardnesses greater and less than that of the workpiece surface and those interstices which are unoccupied by said abrasive particles intercommunicating to define a continuous throughway extending between a rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through said pad for washing liquid applied thereto, effecting relative rubbing movement between said pad and the workpiece, whereby said foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles and said unoccupied interstices in said rubbing surface of said pad, and applying said washing liquid to said rubbing surface of said pad, whereby material worn away from said pad and from the workpiece during the rubbing action will be washed from said rubbing surface of said pad by said washing liquid flowing through said unoccupied interstices in said pad.
 2. A method of grinding according to claim 1 in which said washing liquid is injected through said unoccupied interstices from said face of said pad remote from said rubbing face thereof and said washing liquid is allowed to flow away from said rubbing face through said exposed unoccupied interstices therein.
 3. A grinding tool comprising a pad of reticulated foam-like material having a plurality of interstices therein of which interstices only some are impregnated with abrasive particles, said abrasive particles and said foam-like material respectively having hardnesses greater and less than that of the surface of a workpiece which is to be ground, and those interstices which are unoccupied by said abrasive particles intercommunicating to define a continuous throughway extending between a rubbing surface of the pad and a face thereof remote from said rubbing surface, thereby to define a path through said pad for washing liquid applied thereto, whereby on effecting relative rubbing movement between said pad and the workpiece said foam-like material will be worn away during the rubbing movement to expose fresh abrasive particles and said unoccupied interstices in the rubbing surface of said pad, and a support member in which said pad of foam-like material is mounted, said support member having a port therein through which said washing liquid is passed, said port communicating with said continuous throughway defined in said pad, whereby material worn away from said pad and from the workpiece during the rubbing action will be washed from said rubbing surface of said pad by said washing liquid flowing through said unoccupied interstices in said pad.
 4. A grinding tool as claimed in claim 3 in which said pad is shaped to conform with the surface of the workpiece to be ground.
 5. A grinding tool as claimed in claim 4 in which said pad is pre-shaped before the impregnation of interstices therein with said abrasive particles. 